Processing yield has long been a major concern in integrated circuit (IC) manufacturing. A major cause of IC processing failures is the existence of particles such as dust in the processing environment. Conventional IC processing is therefore done in a clean room in which the air is continuously circulated and filtered in an attempt to remove the airborne particles. In addition, personnel are usually clothed in special suits in an attempt to reduce the number of particles introduced as the workers move about the clean room. As a final step, many of the most vulnerable IC process steps are further contained beneath laminar flow down-drafts of filtered air to provide added protection from local sources of particulate contamination.
Unfortunately such an environment suffers from several disadvantages. First, such specially designed rooms are not only fairly expensive to construct and maintain, but also working in such an environment is inconvenient. Second, since the size of particles which will cause product failure is usually equal to or greater than 1/4 to 1/3 the minimum feature size of the product, it is necessary to continually reduce contamination levels as dimensions are reduced in newer IC products in order to maintain acceptable process yields. This problem becomes especially acute as the minimum feature size drops below one micron for very large scale integrated (VLSI) ICs.